The present invention relates to a two-speed timer.
In timer switches having a maximum set time of, for example, 60 minutes or 120 minutes, it is difficult to set a short operation period, for example, 30 seconds or one minute, because the angle of rotation of the set shaft of the timer is very small for such relatively short periods. Because of this limitation, there have generally been provided two stage timer switches in which the rotational angle of the set shaft, and accordingly the scale thereof, is broadened for such short time settings.
An example of a prior art timer of this general type will be described with reference to FIG. 1. In this timer, a cam wheel b is secured to a set shaft a. The cam wheel has a recess portion related to high speed operation and a convex portion related to low speed operation. A speed change lever c is in frictional contact with the cam wheel. According to the rotation of the set shaft a, when the speed change lever c is in contact with the recess portion of the cam wheel, an idler gear d mounted on the speed change lever c is engaged with a drive reduction gear e, whereas when the speed change lever c is in contact with the convex portion of the cam wheel, the idler gear is disengaged from the reduction gear to thereby perform a change-over of speed.
In such a timer switch, the maximum rotational angle of the set shaft is generally about 300.degree. with the speed change angle being about 200.degree.. If it is desired to change the speed change angle, it is possible to do so by modifying the timer by using a common cam wheel only in the range of .+-.30.degree.. However, beyond this range, an entirely different cam must be manufactured.
In the prior art timer, since the engagement and disengagement between the idler gear d and the reduction gear e are carried out by a radial movement, a strong coil spring f must be used in order to obtain a sufficient engagement pressure between the gears. This leads to a requirement that a great amount of rotational force or torque be used for operation of the set shaft a. At the same time, when the lever c is moved against the spring force, a high load is imposed on the motor (not shown).
Accordingly, an object of the present invention is to provide a timer with a simpler construction than the prior art device and to provide a timer which overcomes the above-noted drawbacks.